Aldehydes, Ketones and Carboxylic Acids

Step 1: Hydrogenation (H₂/Pd-C)
Propyne (CH₃-C≡CH) undergoes partial hydrogenation to form propene (CH₃-CH=CH₂).

Step 2: Ozonolysis (O₃/Zn, H₂O)
Ozonolysis cleaves the C=C bond in propene, producing:
- Ethanal (CH₃CHO)
- Formaldehyde (HCHO)

Thus, the correct answer is: (A) Ethanal and Formaldehyde.

Cannizzaro Reaction:
- Cannizzaro reaction occurs in aldoses (aldehydes with no $\alpha$-hydrogen).
- Acetaldehyde $\left(C{H}_{3}CHO\right)$ has an $\alpha$-hydrogen, so it does NOT undergo the Cannizzaro reaction.
- Acetone $\left(C{H}_{3}COC{H}_3\right)$ is a ketone and also does not undergo the Cannizzaro reaction.
Tollen's Test:
- Tollen's test detects aldehydes (it oxidizes them to carboxylic acids).
- Acetaldehyde $\left(C{H}_{3}CHO\right)$ is an aldehyde, so it gives a positive Tollen's test.
- Acetone $\left(C{H}_{3}COC{H}_3\right)$ is a ketone, and ketones do not give Tollen's test.

Electron-donating groups decrease the electrophilicity of the carbonyl carbon, making it less reactive. On the other hand, electronwithdrawing groups increase the electrophilicity, making the carbonyl carbon highly reactive towards nucleophiles. . Thus, the correct order of increasing reactivity is: acetophenone < p-tolualdehyde < benzaldehyde < p-nitrobenzaldehyde

The Aldol Condensation involves the reaction of two aldehydes or ketones (with at least one alpha-hydrogen) in the presence of a base, leading to the formation of a β-hydroxy ketone or aldehyde, which may further undergo dehydration to give an α,β-unsaturated carbonyl compound. Acetaldehyde can undergo aldol condensation because it has an alpha-hydrogen. Acetone can also undergo aldol condensation since it has alpha-hydrogens as well. Both acetaldehyde and acetone undergo aldol condensation. The Tollen's test detects aldehydes, which are oxidized to carboxylates while the Tollen’s reagent (silver ammonia complex) is reduced to metallic silver. Acetaldehyde can undergo Tollen's test because it is an aldehyde. Acetone cannot undergo Tollen’s test because it is a ketone and does not react with Tollen's reagent. Only acetaldehyde undergoes Tollen's test. The Clemmensen Reduction involves the reduction of ketones or aldehydes to alkanes using zinc amalgam in the presence of hydrochloric acid. Acetaldehyde can undergo Clemmensen reduction to form ethane. Acetone can also undergo Clemmensen reduction to form propane. Both acetaldehyde and acetone undergo Clemmensen reduction.

The given reaction sequence involves:

1. C₆H₁₂ → A (Se/Δ): Dehydrogenation converts cyclohexane to benzene (A = C₆H₆).
2. A → B (AlCl₃/CH₃Cl): Friedel-Crafts alkylation forms toluene (B = C₆H₅CH₃).
3. B → C (CrO₂Cl₂/H₃O⁺): Etard oxidation converts toluene to benzaldehyde (C = C₆H₅CHO).

Checking options:

• C does not give Fehling’s test (A).
• C is not formed from PhMgBr + CO₂ (B).
• C gives Tollen’s test due to the –CHO group (C ).
• C does not react with NaHCO₃ (D).

Final answer: (C) ‘C’ gives Tollen’s test.

Electronwithdrawing group facilitates the nucleophilic addition reaction by increasing electrophilicity on carbonyl carbon, where as electrondonating group decreases reactivity. Hence, the correct order is as follows :

p-Nitrobenzaldehyde >Benzaldehyde>p-Tolualdehyde> Acetophenone